Electromagnetic coupling apparatus



July 4, 1967 V R. JAESCHKE 3,329,247

ELECTROMAGNETIC COUPLING APPARATUS FIG],

VOLTAGE MULTIPLIER k CONTROL 30 Filed 0ct 6, 1965 U CH I c B l D47 0F 0509 ll 01 cm United States Patent 3,329,247 ELECTROMAGNETIC COUPLINGAPPARATUS Ralph L. Jaeschke, Kenosha, Wis., assignor to Eaton, Yale &Towne, Inc., a corporation of Ohio Filed Oct. 6, 1965, Ser. No. 493,39611 Claims. (Cl. 192-84) The present invention relates to electromagneticcoupling apparatus and more particularly to such apparatus whichprovides a rapid buildup of torque transmitted between relativelyrotatable members of a coupling.

It has previously been proposed to obtain rapid buildup of a giventransmitted torque in electromagnetic coupling apparatus by initiallyenergizing the coupling at a higher voltage than that which issubsequently applied to maintain the transmission of the given torque.The arrangements proposed, however, include complicated switchingcircuits for applying power from two different sources during thedifferent phases of energization of the coupling, or employing seriesresistors to effect a voltage drop after an initial energization of thecoupling. The provision of the switching components and the secondsupply considerably increases the expense of the apparatus. The use ofresistors has the disadvantage of power loss and dissipating the heatthereby produced.

Among the several objects of the invention may be noted the provision ofelectromagnetic coupling apparatus which provides exceptionally rapidinitial energization Without complicated switching arrangements; theprovision of such apparatus which does not incur substantial powerlosses; the provision of such apparatus which does not require the useof separate power supplies for initial and for sustained energization ofa coupling; the provision of such apparatus in which a clutch and abrake may be alternately energized to effect accelerated rates ofactuation; the provision of a method for energizing the field coil ofsuch apparatus to provide accelerated actuation of the apparatus; andthe provision of such apparatus which is simple, reliable andinexpensive. Other objects and features will be in part apparent and inpart pointed out hereinafter.

Briefly, the invention is applicable to electromagnetic couplingapparatus having a pair of relatively rotatable members and a fieldcoil, the energization of which controls the transmission of torquebetween the two members. The coil is energized to obtain a rapid buildupof a given torque between said members by a control including a voltagemultiplier which develops a voltage of a first level under no-loadconditions and which under the sustained load of said coil drops to asecond level of voltage substantially lower than this first level. Thesecond voltage level is one which is sufiicient to maintain the coilenergized for the steady state transmission of the given torque. Thecoil is selectively connected by a switching device or means to avoltage multiplier. The multiplier includes means for storing energy atsaid first voltage level when disconnected from the coil. Uponconnection of the coil to said multiplier, the coil is initiallyoverexcited by being energized at the first voltage level and therebyrapidly builds up said given torque and, after discharging of storedenergy, the coil continues to be energized at this second voltage levelto maintain. the transmission of said given torque. The termelectromagnetic coupling apparatus as used herein includes apparatuswherein torque is controllably transmitted between a pair of relativelyrotatable members whether it is either or both of the members whichrotate. Examples of such apparatus are clutches, brakes anddynamometers.

The invention accordingly comprises the apparatus and methodshereinafter described, the scope of the invention being indicated in thefollowing claims.

In the accompanying drawingsin which several of various possibleembodiments of the invention are illustrated,

FIG. 1 is a diagrammatic illustration of an electromagnetic couplingapparatus of the present invention;

FIG. 2 is a schematic diagram of circuitry for controlling the operationof the apparatus of FIG. 1 including means for providing acceleratedactuation of the clutch and brake;

FIG. 3 is a schematic diagram of modified control circuitry providingaccelerated actuation of the brake alone;

FIG. 4 is a schematic diagram of a modification wherein the clutch isenergized at a lower voltage level than either the initial or sustainedenergization level of the brake;

FIG. 5 is a schematic diagram of a circuit for controlling operation ofan electromagnetic brake to provide extreme decelerations; and

FIG. 6 is a schematic diagram of another embodiment of this invention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

Referring now to the drawings, there is shown diagrammatically in FIG. 1electromagnetic coupling apparatus of a type with which the control ofthe present invention is particularly useful. The electromagneticcoupling apparatus comprises both a clutch 11 and a brake 13 which arepreferably of the friction type and are arranged for controlling thespeed of rotation of a driven shaft 15, taking rotational energy from amotor 17.

The shaft of motor 17 is connected to a clutch driving 7 member which inthe present case is illustrated as a rotating electromagnet assembly 19including a field coil or winding 21. Current is supplied to the coil 21through suitable slip rings (not shown). A disc-like armature 23 ismounted on the output or driven shaft 15 for rotation therewith.Armature 23 is positioned within the field of electromagnet assembly 19so that when the coil 21 is energized armature 23 will be drawn intofrictional engagement with driving member 19. Thus torque may beselectively transmitted between the members 19 and 23 by controlling theenergization of coil 21.

The brake 13 is similar in construction to clutch 11 and includes anarmature 24 and an electromagnet 25 wound with a field coil or winding27. However, in the case of the :brake, the electromagnetic structure isstationary and does not rotate, being attached to the frame or otherstationary reference point as at 29. When winding 27 is energized, thearmature 24 is drawn into frictional engagement with the electromagnet25' so that a braking torque is exerted between electromagnet 25 and theshaft 15.

Due to the inductance of the windings 21 and 27 and also to theproduction of eddy currents in the typically unlaminated magneticmembers of the clutch and brake, neither of these devices operatesimmediately upon the application of a voltage across the respectivecoil. Rather, a significant period of time elapses before the currentflowing in the coil and the torque transmitted through the couplingreach their steady state levels. To obtain a more rapid buildup ofcurrent and torque, the coils 21 and 27 are energized by a voltagemultiplier control 30. As described in greater detail hereinafter, thiscontrol overexcites a coil by initially energizing it with a voltagehigher than that which is required to maintain the energization of thecoil for steady state transmission of the desired torque. This initialoverexcitation is provided without the use of a plurality of powersupplies and without timed switching means for effecting the changeover.

FIG. 2 illustrates a control circuit according to the invention whichprovides accelerated energization of both the clutch and the brake coils21 and 27, respectively. The clutch and brake coils are energized byseparate power supplies each of which includes a voltage multiplierconstituted by a voltage-doubling rectifier circuit drawing power froman A.C. power source represented by a pair of A.C. supply lines L1 andL2. The brake power supply includes a pair of rectifiers or diodes D1and D2 which are connected to supply line L1 and are oppositely poled ororiented so that each provides half-wave rectified or pulsating D.C. toone of a pair of filter and storage capacitors C1 and C2. One terminalof each capacitor is commonly connected to line L2. Due to the opposedpolarities of the diodes D1 and D2 the capacitors C1 and C2 are chargedto opposite D.C. potentials with respect to supply line L2 duringalternate half cycles of the applied A.C. power. Thus, this circuitfunctions as a voltage doubler, the voltage produced under no-loadconditions across capacitors Cl and C2 together, or in series, beingapproximately double the peak supply voltage. The brake coil 27 isselectively connected across capacitors C1 and C2 by a set of contacts81A of a switch S1 which may, for example, be an electromagneticallyoperated relay.

The clutch coil power supply includes a similar voltage doubler whereina pair of capacitors C3 and C4 are alternately charged to oppositepotentials with respect to supply line L2 through a pair of oppositelypoled diodes D3 and D4 connected to line L1. The clutch coil 21 isselectively connected across the series-connected capacitors C3 and C4by means of a pair of contacts 81B of switch S1.

The voltage regulation characteristics of voltage multiplier circuitsare typically quite poor in the sense that the voltage provided underloading is significantly lower than that provided under no-loadconditions. The regulation characteristics depend to a large extent onthe value of the capacitors used. In the apparatus illustrated in FIG.2, the ratings of the clutch and brake coils 21 and 27 are chosen sothat the voltage required for full, steady state energization thereof issubstantially below the peak voltage provided by the respectivevoltage-doubling power supplies. For example, in apparatus supplied fromA.C. mains providing A.C. at 110 volts R.M.S., or approximately 150Volts peak value, the voltagedoubling power supply for the clutch coil21 will, under no-load conditions, charge the capacitance constituted byseries-connected capacitors C3 and C4 to a total voltage ofsubstantially 300 volts. The clutch coil 21 may, for example, have acontinuous energization rating of about 50 volts. The values of thecapacitors C3 and C4 are then chosen so that the voltage supplied by thedoubler circuit to the clutch coil under conditions of continuousenergization is approximately 5.0 volts, a level which will permit theclutch coupling to continuously maintain the rated torque transferbetween the relatively rotatable components thereof.

When the clutch coil 21 is not connected to its power supply, however,the capacitors C3 and C4 become charged so that the total voltage acrossthem reaches approximately 300 volts and a significant quantity ofenergy will thus be capacitively stored at this voltage level.Accordingly, when the clutch coil 21 is initially connected across itspower supply by the closing of contacts SIB, the stored energy willoverexcite the clutch coil 21 at this higher voltage level so that itbecomes fully energized and capable of transmitting its rated torquemuch more rapidly than it would if a voltage only equal to its sustainedenergization rating were applied. The stored energy will provideoverexcitation for only a relatively short time and thus, after apredictable delay interval, the voltage provided by the doubler circuitwill drop or sag to the level which the doubler is capable of supplyingunder steady state load conditions. This level is, as noted previously,selected by choice of value for capacitors C3 and C4 to be substantiallyequal to the rated voltage of the clutch winding 21.

A similar situation exists with respect to the brake coil 27. That is,the capacitors C1 and C2 are chosen to provide a steady state voltagewhich is equal to the sustained energization rating of brake winding 27.However, when the brake winding is disconnected from its power supplythese capacitors will be charged to a voltage which is substantiallydouble the peak voltage supplied by the lines L1 and L2. Thus, uponinitial connection of brake coil 27 to its power supply by the closingof switch contacts S1A, the brake coil will be initially overexcited,thereby providing an accelerated braking operation. After discharging ofcapacitively stored energy, coil 27 will subsequently be maintainedenergized by a voltage substantially equal to its sustained energizationrating.

While the clutch and brake power supplies exhibit socalled soft voltageregulation characteristics, it should be noted that the drop in voltageupon loading is not due to resistive dissipation which would causesubstantial power losses and create heat dissipation problems. Rather,the difierence in voltage arises because of reactive voltage dropsdeveloped across capacitive elements, which voltage drops do not entailsignificant power loss.

Under certain circumstances only one of the two coupling coils needs tobe initially overexcited or electrically forced to obtain acceleratedenergization while the other coil need be energized only at its ratedvoltage. In FIG. 3 the brake coil 27 is again connectable across theoutput of the voltage doubler comprising diodes D1 and D2 and capacitorsC1 and C2. The clutch coil 21, however, is not provided with a separatevoltage doubler power supply but rather is connectable, through contactsSIB, across one (C2) of the two capacitors used in the brake coil powersupply. Thus clutch winding 21 is provided only with half-wave rectifiedpower and does not draw from any voltage doubler or multiplier circuit.Accordingly, clutch coil 21 is chosen to have a sustained voltage ratingapproximately equal to the value of the half-wave rectified A.C.provided by lines L1 and L2 and rectifier D2. In operation, the controlof FIG. 3 thus provides essentially normal operation of clutch coil 21but will, due to the voltage drop characteristics of the doubler powersupply, pro vide an initial overexcitation of brake winding 27 so thatrapid decelerations of shaft 15 may be obtained. However, due to thefact that half of the doubler circuit is never under no-load conditions,the ratio of peak to full-load voltages will not be as great as thatobtained using the circuitry of FIG. 2.

Another arrangement wherein only one of the coupling coils is initiallyoverexcited is illustrated in FIG. 4. In this embodiment, the brakewinding 27 is selectively connectable by means of contacts 81A to thevoltage doubler power supply comprising diodes D1 and D2 and capacitorsC1 and C2, the doubler power supply again being supplied from lines L1and L2 with line L1 providing A.C. power at a first voltage level withrespect to line L2.

The clutch winding 21 is connected to receive halfwave rectified powerthrough a diode D5 and switch contacts S1B from a supply line L1A whichprovides A.C. power at a second preselected level with respect to lineL2. The peak voltage present at line L1A with respect to line L2 ischosen to the less than either the initial voltage at which the coil 27is overexcited or the lower voltage level at which its energization ismaintained. Thus, in operation the brake winding will be initiallyoverexcited to provide rapid stops of the shaft 15 as in the previousexamples but energization of the clutch coil 21 will take place at onevoltage level only, which voltage level is lower than both the initialand sustained voltage levels applied to winding 27. It will beunderstood that the potential difference between L1A and L2 may beselected to be equal to or greater than the L1-L2 voltage.

Voltage multipliers which treble, quadruple, etc. the supply voltagetypically have even poorer voltage regulation characteristics thandoublers. In other words, larger ratios of no-load voltage to full-loadvoltage are en counted. Accordingly, by employing circuits using evenhigher degrees of voltage multiplication in controls according to thepresent invention, even more rapid accelerations may be obtained. In thecontrol illustrated in FIG. the brake winding 27 is energized from avoltage quadrupler power supply which comprises a series string ofdiodes D6-D9. A plurality of capacitors C6-C9 couple A.C. to each of therectifiers in the string from the lines L1 and L2. Under no-loadconditions, this supply will develop a voltage which is substantiallyequal to four times the peak voltage appearing across the supply linesL1 and L2. The capacitors C6 C9 will be charged and will thus representa quantity of stored energy avialable for intially overexciting winding27 at the higher voltage upon its initial connection to the supply. Uponcontinued connection of coil 27 to this multiplier power supply,however, the voltage applied to the winding will drop to a much lowervalue, the level of which is in large part determined by the individualcapacity values of the capacitors C6-C9. By proper choice of thesecapacitance values the steady state voltage provided by the supply maybe made approximately equal to the rated voltage of the coil 27 eventhough this value is very small in relation to the peak voltageinitially provided by the quadrupler supply. Accordingly, it can be seenthat the control of FIG. 5 is capable of providing a very high degree ofinitial overexcitation for extremely rapid operation of the brake. Itshould be understood that a clutch coil could be similarly operated andthat both a clutch and brake may be alternately operated in this mannerfrom separate voltage multiplier supplies in the manner illustrated inFIG. 2.

FIG. 6 illustrates a control which is similar to that shown in FIG. 5.The voltage multiplier which supplies power to winding 27 is again aquadrupler which includes diodes D6-D9 connected in a series string. Aset of capacitors C11C14 couples A.C. to each of the rectifiers.However, A.C. is coupled to the higher voltage rectifier stages bycapacitors which draw power from the lower voltage stages rather thandirectly from the lines L1 and L2. Accordingly, under load, theseries-connected capacitors act as A.C. voltage dividers which cause aneven greater drop in the output voltage. Thus, when used in a controlaccording to the present invention this multiplier circuit permits anincreased ratio of initial excitation voltage to sustained energizationvoltage.

While various particular voltage multipliers are shown by way ofillustration, it is to be understood that there are other such circuitswhich provide substantially different levels of voltage under no-loadand full-load conditions and do not involve substantial dissipation ofpower within the supply under loaded conditions, and such circuits maybe used in the practice of the present invention. Similarly, whileelectromagnetically controlled friction clutches and brakes have beenshown, other types of electromagnetic couplings which normally respondonly after a delay following energization, such as eddycurrentcouplings, may advantageously employ the present invention. Also, two ormore clutches may be alternate- 1y employed to drive a load from shaftsrotating at different speeds or in opposite directions.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. In electromagnetic coupling apparatus having a pair of relativelyrotatable members and a field coil the energization of which controlsthe transmission of torque between the two members; a control forobtaining rapid buildup of a given torque between said members, saidcontrol comprising:

a voltage multiplier which develops a voltage of a first level underno-load conditions and which under the sustained load of said coil dropsto a second level of voltage substantially lower than said first level,said second voltage level being sufiicient to maintain said coilenergized for the steady state transmission of said given torque; and

switching means for selectively connecting said coil to said voltagemultiplier, said multiplier including means for storing energy at saidfirst voltage level when said coil is disconnected therefrom whereby,upon connection of the coil to said multiplier, said coil is initiallyoverexcited by being energized at said first voltage level thereby torapidly build up said given torque and, after discharging of storedenergy, said coil continues to be energized at said second voltage levelto maintain the transmission of said given torque.

2. Electromagnetic coupling apparatus providing rapid buildup of a giventransmitted torque, said apparatus comprising:

an electrically controllable coupling including a pair of relativelyrotatable members and a field coil the energization of which controlsthe transmission of torque between the two members;

a voltage multiplying rectifier circuit for providing DC. power forenergizing said coil from an A.C. power source, said rectifier circuitincluding a capacitance and being operative when said coil isdisconnected therefrom to charge said capacitance to a first voltagewhich is substantially higher than the steady state voltage which saidcircuit can maintain across said coil, said steady state voltage bein-gsufiicient to maintain said coil energized for the transmission of saidgiven torque; and

switching means for selectively connecting said coil to said rectifiercircuit whereby, upon connection of the coil to said circuit, said coilis initially overexcited by being energized at said first voltage levelthereby to rapidly build up torque and, after discharging of energystored in said capacitance, said coil continues to be energized at saidsteady state voltage to maintain the transmission of said given torque.

3. Apparatus as set forth in claim 2 wherein said relatively rotatablemembers are frictionally engageable and are magnetically drawn intoengagement by energization of said field coil.

4. Apparatus as set forth in claim 2 wherein said capacitance comprisesat least two capacitors and said rectifier circuit includes at least tworectifiers through which said capacitors are alternately charged.

5. Apparatus as set forth in claim 2 wherein said volt-, age multiplyingrectifier circuit comprises:

first and second capacitors constituting said capacitance, one terminalof each of said capacitors being commonly connected to one side of saidA.C. source;

first and second rectifiers each of which connects the other terminal ofa respective one of said capacitors to the other side of said A.C.source, said rectifiers being oppositely oriented whereby saidcapacitors are charged to voltages of opposing polarities with respectto said oneside of said source, said switching means being operative toconnect said coil across said two capacitors in series.

6. Apparatus as set forth in claim 5 wherein said electricallycontrollable coupling includes a third relatively rotatable member and asecond field coil the energization of which controls the transmission oftorque between said third member and one of the other members andwherein said switching means includes means for selectively connectingsaid second coil across one of said two capacitors.

7. Apparatus as set forth in claim 2 wherein said electricallycontrollable coupling includes a third relatively rotatable member and asecond field coil the energization of which controls the transmission oftorque between said third member and one of the other said members, andwherein said apparatus includes a second voltage multiplying rectifiercircuit for energizing said second coil, and wherein said switchingmeans includes means for selectively connecting said second coil to saidsecond rectifier circuit for energization alternately with the firstsaid coil.

8. Apparatus as set forth in claim 2 wherein said electricallycontrollable coupling includes a third relatively rotatable member and asecond field coil the energization of which controls the transmission oftorque between said third member and one of the other members andwherein said apparatus includes means for selectively energizing saidsecond field coil at a voltage which differs from said first voltage.

9. Apparatus as set forth in claim 8 wherein said differing voltage islower than said steady state voltage.

10. Apparatus as set forth in claim 2 wherein said voltage multiplyingrectifier circuit includes a plurality 25 of rectifiers poled in thesame direction and connected in a series string and a plurality ofcapacitors for coupling A.C. along said string.

11. The method of energizing the field coil of an electromagneticallycontrollable coupling from an AC. source to obtain a rapid buildup of agiven torque between two relatively rotatable members thereof, saidmethod comprising:

rectifying the supplied AC. power in a voltage multiplying circuit;charging a capacitance to the voltage supplied by said rectifyingcircuit, said rectifying circuit being operative under no-loadconditions to charge said capacitance to a first voltage which issubstantially higher than the steady state voltage which said circuitcan maintain across said coil, said steady state voltage beingsuflicient to maintain said coil energized for the transmission of saidgiven torque; and selectively connecting said coil across saidcapacitance thereby to initially overexcite said coil at said firstvoltage to rapidly build up torque and, after discharging of energystored in said capacitance, continuing to energize said coil at saidsteady state voltage to maintain the transmission of said given torque.

References Cited UNITED STATES PATENTS 2,811,686 10/1957 Hill 321-l5 X2,888,629 5/1959 Everhart et al. 321--15 3,254,746 6/1966 Myers 192843,268,045 8/1966 Poumakis 192-84 MARK NEWMAN, Primary Examiner.

ARTHUR T. MCKEON, Examiner.

1. IN ELECTROMAGNETIC COUPLING APPARATUS HAVING A PAIR OF RELATIVELYROTATABLE MEMBERS AND A FIELD SOIL THE ENERGIZATION OF WHICH CONTROLSTHE TRANSMISSION OF TORQUE BETWEEN THE TWO MEMBERS; A CONTROL FOROBTAINING RAPID BUILDUP OF A GIVEN TORQUE BETWEEN SAID MEMBERS, SAIDCONTROL COMPRISING: A VOLTAGE MULTIPLIER WHICH DEVELOPS A VOLTAGE OF AFIRST LEVEL UNDER NO-LOAD CONDITIONS AND WHICH UNDER THE SUSTAINED LOADOF SAID COIL DROPS TO A SECOND LEVEL OF VOLTAGE SUBSTANTIALLY LOWER THANSAID FIRST LEVEL, SAID SECOND VOLTAGE LEVEL BEING SUFFICIENT TO MAINTAINSAID COIL ENERGIZED FOR THE STEADY STATE TRANSMISSION OF SAID GIVENTORQUE; AND SWITCHING MEANS FOR SELECTIVELY CONNECTING SAID COIL TO SAIDVOLTAGE MULTIPLIER, SAID MULTIPLIER INCLUDING MEANS FOR STORING ENERGYAT SAID FIRST VOLTAGE LEVEL WHEN SAID COIL IS DISCONNECTED THEREFROMWHEREBY, UPON CONNECTION OF THE COIL TO SAID MULTIPLIER, SAID COIL ISINITIALLY OVEREXCITED BY BEING ENERGIZED AT SAID FIRST VOLTAGE LEVELTHEREBY TO RAPIDLY BUILD UP SAID GIVEN TORQUE AND, AFTER DISCHARGING OFSTORED ENERGY, SAID COIL CONTINUES TO BE ENERGIZED AT SAID SECONDVOLTAGE LEVEL TO MAINTAIN THE TRANSMISSION OF SAID GIVEN TORQUE.